The invention is-related to the field of encoding digital information signals.
The invention relates to an apparatus for generating a runlength limited (RLL) digital information signal, the digital information signal having a minimum runlength of dxe2x80x2 and a maximum runlength of kxe2x80x2, dxe2x80x2 and kxe2x80x2 being integers larger than zero and where kxe2x80x2 is larger than dxe2x80x2 and to a method for generating such runlength limited digital information signal. The invention further relates to an apparatus for and a method of generating a (d,k) sequence.
Those skilled in the art are directed to the following related documents:
(D1) U.S. Pat. No. 5,477,222 (PHN, 14.448)
(D2) K. A. Schouhamer Immink, Coding Techniques for Digital Recorders, Prentice Hall, 1991.
(D3) P. Funk; Run-Length-Limited Codes with MultipleSpacing, IEEE Transactions on Magnetics, Vol. MAG-18, 1982, pp. 772-775.
(D4) U.S. Pat. No. 5,696,505 (PHN 14.746).
An apparatus as defined in the opening paragraph is eg. known from U.S. Pat. No. 5,477,222, document D1 in the list of related documents.
Runlength limited digital information signals obtained from channel coding an information signal are described in the book coding techniques for digital records by K. A. Schouhamer Immink, Prentice Hall, 1991, chapter 5, document D2. Such runlength limited digital information signals are generally derived from so-called (d,k) constrained sequences. In such sequences, expressed in NRZ-I (non-return-to-zero-inverse) notation, two logical xe2x80x98onesxe2x80x99 in the sequence are separated bva run of consecutive xe2x80x98zerosxe2x80x99 of length at least d, and any run of consecutive xe2x80x98zerosxe2x80x99 is of length at moist k. A (d,k) sequence is normally converted in a precoding step so as to obtain the runlength limited information signal. In such runlength limited information signal obtained from the above (d,k) sequence, minimum runlengths of d+1 of consecutive like symbols occur and maximum runlengths of k+1 consecutive like symbols occur in sequences expressed in NRZ notation. This precoding of a (d,k) sequence, for d=1 and k=7 as an example, results in a runlength limited information signal having a minimum runlength of 2 and a maximum runlength of 8.
A choice of a specific channel code, properly adopted to the physical channel characteristics, is limited by the fact that the d-constraint is restricted to the natural numbers (d=0, d=1, d=2, . . . ). It has been proposed in the past to remove this limitation, by using rational d-constraints. Reference is made in this respect to the publication by P. Funk, document D3 in the list of related documents.
The above documents are hereby incorporated herein in whole by reference.
The invention has for its object to provide a different alternative for an apparatus which is capable of generating channel codes which fill up the gap between d and d+1 for the traditional (d,k)-based codes.
In accordance with a first aspect of the invention, the channel code generating apparatus is adapted to generate the runlength limited digital information signal, such that a minimum runlength in the digital information signal occurs isolated from other minimum runlengths in the digital information signal.
In accordance with a second aspect of the invention, the channel code generating apparatus for generating a runlength limited digital information signal, the digital information signal having a minimum runlength of dxe2x80x2 and a maximum runlength of kxe2x80x2, dxe2x80x2 and kxe2x80x2 being integers larger than zero and where kxe2x80x2 is larger than dxe2x80x2. Also, the channel code generating apparatus is adapted to generate the runlength limited digital information signal, such that a minimum runlength occurring in the digital information signal follows only a directly precedingrunlength larger than dxe2x80x2.
In accordance with a third aspect of the invention, the channel code generating apparatus for generating a runlength limited digital information signal, the digital information signal having a specific minimum runlength and a maximum runlength of kxe2x80x2, the apparatus including first apparatus for generating runlengths in the digital information signal of length dxe2x80x2+1 at minimum, where dxe2x80x2 and kxe2x80x2 are integers larger than zero and where kxe2x80x2 is larger than dxe2x80x2+1. Also, the channel code generating apparatus further includes second apparatus for generating runlengths of dxe2x80x2 in the runlength limited digital information signal, such that such runlengths of dxe2x80x2 occur isolated from other such runlengths of dxe2x80x2 in the digital information signal.
In accordance with a fourth aspect of the invention, the channel code generating apparatus is adapted for generating a runlength limited digital information signal, the digital information signal having a specific minimum runlength and a maximum runlength of kxe2x80x2, the channel code generating apparatus including first apparatus comprising means for generating runlengths in the digital information signal of length dxe2x80x2+1, where dxe2x80x2 and kxe2x80x2 are integers larger than zero and where kxe2x80x2 is larger than dxe2x80x2+1. Also, the channel code generating the apparatus further includes second apparatus for generating runlengths of dxe2x80x2 in the runlength limited digital information signal, such that such runlengths of dxe2x80x2 occur only following a directly preceding runlength larger than dxe2x80x2.
The invention generates (d,k)-based RLL channel codes, with the additional allowance of isolated Id runlengths (that is: isolated runlengths of length d), which are normally forbidden in a pure (d,k) code. An isolated Id runlength has to be surrounded by two other runlengths In with n greater than d. In contrast, for a pure (dxe2x88x921,k) RLL channel code, the appearance of Id""s is unconditional. Therefore, the capacity of the new (d,k) code with isolated Id""s (called for short an iso-Id(d,k) code), is between the capacity of the traditional (d,k) and (dxe2x88x921,k) channel codes. The increase in capacity of the iso-Id(d,k) code compared to the pure (d,k)-code, goes together with an increase in the highest frequency in the bit-sequence, which equals 1/(2d+1) for the iso-(d,k) code, which is between 1/(2d+2) and 1/2d (for the pure (d,k) and (dxe2x88x921,k) codes, respectively).
It is to be understood that, where the claims define a RLL digital information signal with a minimum runlength of dxe2x80x2, dxe2x80x2 should be taken equal to the parameter d introduced above, in order to bring the claims in conformity with the above argumentation.